BP’s long awaited internal investigation into the causes of the Gulf of Mexico oil and gas well blowout blamed “a sequence of failures involving a number of different parties,” but BP chief executive Tony Hayward said the well’s much-criticized well design was probably not among the causes.
The company’s four-month investigation by a team of more than 50 technical and other specialists found that the type of cement slurry that was used failed, along with a device known as a shoe barrier designed to contain oil and gas.
The report, released Wednesday, also said that BP and Transocean workers “incorrectly accepted” the results of a pressure test. And it added that over a crucial 40-minute period, the Transocean rig crew “failed to recognize and act on the influx of hydrocarbons into the well” when it might still have been possible to cut off the flow.
In addition, the report pointed to failures after that point. It said that the gas that surged to the rig should have been diverted overboard but was vented directly onto the rig and then through its ventilation system.
“It is evident that a series of complex events, rather than a single mistake or failure, led to the tragedy,” said BP’s outgoing chief executive Hayward, who has agreed to step down Oct. 1. “Multiple parties, including BP, Halliburton and Transocean, were involved.”
The BP report stressed that “no single factor” caused the April 20 blowout that killed 11 workers, sank the Deepwater Horizon drilling rig and led to the largest oil spill in U.S. history.
The investigative team “did not identify any single action or inaction that caused this accident,” the company said. “Rather, a complex and interlinked series of mechanical failures, human judgments, engineering design, operational implementation and team interfaces came together to allow the initiation and escalation of the accident. Multiple companies, work teams and circumstances were involved over time.”
Before the report was issued, BP executives said for months that it was too soon to say why the rig exploded. The new report comes as other investigations continue, including a Justice Department criminal probe.
The internal inquiry began just days after the blowout, as BP investigators questioned the well site leaders, Donald Vidrine and Robert Kaluza, the “company men” who were on board the rig at the time of the explosion. Neither has testified publicly or given interviews.
The investigation also probed the design of the well, the maintenance of the blowout preventer that failed to choke the well at the crucial moments, and the decision by BP executives to proceed with a cement job despite a report by the contractor, Halliburton, stating that the well as designed was potentially subject to a “severe” gas flow problem.
Prior to the new BP report, the general outline of what happened has been clear for months. The exploratory well, named Macondo by BP, had been a difficult drilling job in 5,000 feet of water in the Gulf of Mexico. The Deepwater Horizon, owned by Transocean and leased by BP, was weeks overdue for its next drilling assignment. The blowout took place in the final stages of the plugging and temporary abandonment of Macondo. Federal investigators have probed whether the company took short cuts or made safety-related decisions with cost in mind.
Halliburton employees had cemented the well, but BP did not choose to run a “cement bond log” test that might have detected whether there were fissures in the cement that could have given gas an avenue to the surface.
Then, on the afternoon of April 20, BP ran two pressure tests that, in retrospect, clearly signaled that gas was flowing in the well and that BP had a serious well-control problem on its hands. But rather than shutting in the well at that point, the leaders on the rig interpreted the tests as benign. They continued to remove heavy drilling mud from the well and replace it with much lighter sea water. That’s when the blowout happened.
The other companies involved have yet to give their version of events, and Transocean has pointedly complained that BP hasn’t turned over data that would help Transocean with its own internal investigation.
